Wireless-telegraph system.



No. 806,966. PATENTED DEC. 12, 1905. L. DE FOREST.

WIRELESS TELEGRAPH SYSTEM.

APPLICATION FILED JAN. 25, 1904. RENEWED 001 .14.1905.

Fig, 1. e

Fl'g. 2.

WITNESSES: I IN VENTOf? Lee deForeM.

Wig

UNITED STATES PATENT OFFICE.

WlRELESS-TELEGRAPH SYSTEM.

Specification of Letters Patent.

Patented Dec. 12, 1905.

Application filed January 25, 1904. Renewed October 14, 1905- Serial No. 282,811.

To all whom it may concern.-

Be it known that 1, LEE DE FOREST, a citizen of the United States, and a resident of the city, county, and State of New York, have invented certain new and useful Improvements in VVireless-Telegraph Systems, of which the following is a specification.

My invention relates to improvements in wireless-telegraph systems.

The object of my invention is to improve and simplify the construction and operation of such systems.

My invention will be defined hereinafter and particularly in the claims.

In the accompanying drawings I have shown systems containing my invention, the same corresponding with the constructions which are now preferred by me.

Figure 1 illustrates the action of an openend antenna or radiator. Fig. 2 illustrates a closed-circuit antenna or resonator. Figs. 3 and 4 illustrate systems embodying my invention.

It is well known that to secure electrical tuning or resonant effects it is desirable to prolong as far as possible the number of oscillations excited in a resonant system, in other words to reduce as much as possible the damping-factor.

For high-frequency electrical oscillations,

resonant circuits may be of two types, known.

as closed and open circuits. Electrostatic loops will occur at the open ends of the latter type, and nodes at points in the circuit which correspond to a difference of phase of ninety degrees in the electrical oscillation.

In the simplest case of a straight conductor, open at both ends and subjected in any manner to a sudden electrical impulse, surgings will be set up in the conductor, and the reflection which these electrical surgings or oscillations experience at either open end of the conductor will cause a loop of static force to be formed at either'end, with a static node, or

electromagnetic loop at a point midway between. This condition is illustrated in Fig. 1 where a I) represent a rectilinear conductor vibrating as an electrical resonator. The distribution of electrostatic stress throughout the length of the conductor, due to the reflection at the ends of the electrical surgings induced or set up in the conductor, is illustrated by the curved line, d, c, 6. At 0 is found a static node, i. e. a point where the resultant electromotive force of the oscillations set up in the conductor, is zero. At this point also, the cur- .surgings are induced therein.

rent flowing is maximum. In other words at 0 will be found an electromagnetic loop. Now if this rectilinear conductor be bent into circular form, as in Fig. 2, so that the two ends, a and 6 are nearly in contact with each other, the same conditions hold as before when electrical We have a condenser action between a and b where exist static loops of opposite signs, and mid way between, at c, a static node.

Now it can be shown that a closed resonator is a far more persistent oscillator, one less strongly damped, and therefore adapted to much closer tuning, than is the open-end type. At the same time it is a poorer radiator and therefore can pick up and respond to weak or a periodic oscillations less readily than the open end type of oscillator.

The closed resonator-circuit containing the receiving or wave-sensitive device, has been useful to attune the natural period of vibra' tion of this'antenna or wave-receiving system with the closed and more highly resonant system at its base, which latter system contains the wave responsive or sensitive member. This tuning however cannot be very accurate or close for the very reason that the antenna in itsusual open-end form is a strongly-damped resonator, with its own distinctive period of vibration poorly defined. Electrical vibrations set up therein by the passage of a train of waves from the distant transmitting-station are not only passed on into the closed resonant-circuit containing the wave-responsive device at the lower end of the anthma but the vibrations set up in the antenna are also actually dissipated into space therefrom,the antenna acting as a secondary radiator.

I have discovered a method of construction of and connection for the antenna which while still allowing it to retain its upright, essentially rectilinear character best adapted to catching or picking up transmitted wave trains, yet enables it to become for the received oscillations a poor radiator, and enables it to have all the advantages of the closed-circuit, conservative type of resonators, Whose natural period of vibration is strongly defined. So marked is the advantage obtained from this arrangement of antenna-circuit that I am able thereby to increase by several times the intensity of the effect of the impulses upon the wave-responsive device, over that possible with the usual, open-end antenna employing the very best known closed, resonant-tuning circuits at its base. The principle of the arrangement employed is shown in Figs. 3 and 4, wherein the antenna A consists of two parts (each of which may comprise one or more conductors) joined together at the top but insulated at the base, one branch leading off to the left, through the helix 0 ordinarily employed for syntonic purposes in the transmitting-circuit, and thus to earth E, the other, or righthand branch, leading off through another syntonizing-helix' T to the receiver R, and thence also to earth E. There is formed thus acompletely-closed electrical circuit, connected at one point, (where must therefore be formed a'static node,) to earth. This closed circuit must needs vibrate as a half-wave length, or a multiple thereof, of the oscillation set up therein. Attention is called to the fact that the usual open-end antenna vibrates as a quarter-wave length. Unless impedance, such as shown at 0 be inserted in that branch of the antenna not leading to the receiver, R, I find that the greater part of the electrical impulse seeks that path to earth, and, there being then no electrical momentum, no prolonged oscillations can be set up in the closed circuit. But even so small an inductance as is generally required to insert in the closed oscillating circuit of the transmitter O S C 0, e. g. two turns of a helix twelve inches in diameter, will cause the closed receiving and antenna circuit E 0 g a 6 W p T R C E to respond strongly to the passing train of waves, provided the period of this circuit be in tune with that of the electrical-wave train. To accomplish this tuning of the above-described circuit I insert between the right-hand branch of the antenna and the receiver, (or resonantcircuit containing the receiver) an adjustable tuning-helix T, wherein, by means of the sliding contact-point p, or by other well-known means, the inductance may be readily altered.

W is a switch which is opened when the station is used for transmitting, to prevent the powerful oscillations of the antenna from running through the helix T and damaging the same or the receiver R.

C is a condenser of sufficient capacity to offer no appreciable impedance to the highfrequency electrical oscillations employed, and yet preventing the flow of local current through the antenna-circuit, which would thus short-circuit the receiver. If desired the capacity of C may be adjusted for syntonizing purposes.

g is a small spark-gap so arranged that when used as a transmitter both halves of the antenna will act as one, or'as if metallically connected at the base, yet compelling the antenna to act as a loop in receiving. This spark-gap g is so small that when the transmitting apparatus-is in operation, the powerful highfrequency oscillations of the large spark S readily jump across the small gap 9, so that both-sides a and b of the loop act as a single open-ended antenna as if the lower ends of at and b were electrically connected together. But when the transmitting apparatus ceases operation, and the switch W is closed to connect in the receiving apparatus, the signal impulses received from a distant transmitting apparatus are so feeble that they cannot jump across even the small spark-gap g; and thus these feeble received impulses are compelled to traverse the loop a, b in receiving. In the case shown, it is the spark-gap g which insulates the bases of the loop from each other,

but they may be otherwise insulated from each other.

I find that although one or two turns in the oscillating transmitter-helix O is sufficient to put both the closed oscillatingtransmittercircuit 0 S C O, and the antenna earth-circuit, A g 0 E, into syntony, and at the same time, as described above, to compel the closed receiver-circuit to pickup and respond to the transmitted wave-train, yet it is at times olesirable to have approximately as much inductance in the left-hand branch of the antenna-loop as in the right-hand branch. Consequently I may insert in the main ground-' lead 0 E a small spark-gap S and shunt same by a third adjustable helix T. The impedance of this helix can be adjusted along with that of T, to put the receiver-circuit in perfect syntony with the received oscillations. At the same time its impedance is so great that the powerful transmitter oscillations will jump the small spark-gap S by preference. In this way the impedance of T will not figure in determining the natural period of the transmitter oscillation.

Fig. 3 shows the receiver R directly in the antenna-circuit. It is at times desirableto put the receiver in a secondary closed circuit, likewise tuned to the desired frequency, in order to still further guard it from undesired impulses. Such an arrangement is shown in Fig. 4 where two sliding points lead off from the helix T, one to a branch of the antenna-loop, the other through the condenser 0 and receiver R,'to the earth connection. Thus the receiver is in a second closed circuit 19 q C R p, the period of whose vibration can be adjusted by moving the point q as well as the point p. Thus the antenna-loop circuit can be syntonized with the desired transmitted impulses and then the second receivercircuit again syntonized with the antenna-loop circuit.

By the principle herein described I am able to greatly increase the volume of sound in a receiver-telephone, eliminate to a greater IIO degree than by any previous method of tuning all outside interferences, and increase greatly the range over which, with a given transmitter and receiver, it is possible to transmit reliable .and accurate signals. This principle of the closed antenna-circuit in receiving, at-

tuned to the desired frequency, may obviously be adapted to a variety of specific circuits,

4 but the advantage in all cases to be derived is dueto the fact that the antenna, which has previously in the art been a strongly-damped radiator, is transformed into a persistent, energy-conserving resonator, yet without in the least impairing its adaptability to the picking up or catching of the desired transmitted impulses. At the same time it may be readily transformed into a strong radiator when used for transmitting.

I do not wish to be limited to the specific methods of connections herein shown as these may obviously be widely varied without departing from the essential features of my invention.

What I claim is 1. In an electric-wave signaling system, the combination with an antenna-loop, joined at the top but insulated at the base; of a closed electric circuit connected to the antenna baseterminals; transmitting and receiving means operatively associated with the closed electric circuit; and a spark-gap constructed and ar- 'ranged topermit both sides of the antennaloop to act as a single transmitting-radiator, and also to enable the antenna to act as a loop in receiving. I

2. In an electric-wave signaling system, the combination with an antenna-loop, joined at the top but insulated at the base, of a closed electric circuit connected to the antenna baseterminals; an adjustable tuning-helix connect-. ed in one branch of said closed electric circuit; and in the same branch, asecond adjustable tuning-helix shunted by a spark-gap; an adjustable helix in the other branch of said closed electric circuit; and a receiving device operatively associated with said closed electric circuit.

3. In an electric-wave signaling system, the combination with an antenna-loop, joined at the top but insulated at the base; of a closed electric circuit connected to the antenna baseterminals; a tuning-helix in said closed circuit, a second closed circuit operatively associated with said closed electric circuit; a tuning-helix in said second closed circuit, a receiving de-- vice in said second closed circuit; means for adjusting said helix in the first closed circuit; and means for adjusting said helix in the second closed or receiver circuit.

4. In an electric-wave signaling system, the combination with an antenna-loop, joined at the top but insulated at the base; of a closed electric circuit connected to the antenna baseterminals; a receiver operatively associated with said closed circuit; and an impedance- 6. In an electric-wave signaling system, the Y combination with an antenna-loop, joined at the top but closed at the base; of a closed electric circuit connected to the antenna base-terminals, and forming with the antenna-loop, a

closedcircuit equivalent in length to a halfwave length or a multiple thereof; an adjustable tuning-helix in one branch of said closed circuit; a second adjustable helix in the other branch of said closed circuit; and a receiving device operatively associated with said closed electric circuit.

7. A wireless signaling system comprising two antennae connected at one end, separate connections from the other end of each to the earth, adjustable tuning devices in each of said connections, and a receiving mechanism connected with one of said connections.

8. 'A wireless signaling system comprising two antennae electrically connected at one end, separate connections from their other ends to the earth or capacity, a transmitting mechanism connected with one of said earth connections, a receiving mechanism connected with the other earth connection, adjustable tuning devices connected with each of said earth connections, and means for cutting out thereceiving mechanism when sending.

9. A wireless signaling system comprising two antennae connected at one end, a waveproducing mechanism connected with one antenna,a signal-receiving mechanism connected with the other antenna, a ground connection and means for disconnecting the latter mechanism from the antennae.

10. In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected at the top but insulated at its base-terminals specifically by a spark-gap; of an electric circuit connected to the antenna-terminals and forming with the antenna-loop acloscd circuit; transmitting and receiving means operatively associated with said closed circuit; and means for cutting out the receiving means while the transmitting means is in use.

11. In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected at the top but insulated at its base-terminals specifically by a spark-gap; of an electric circuit connected to the antenna-terminals and forming with the antenna-loop a closed circuit; a secondary closed circuit including transmitting appara- IIC tus and operatively associated with the first closed circuit; a secondary closed circuit including receiving apparatus and operatively connected with the first closed circuit; and

means for cutting out the receiving means while the transmitting means is in use.

12. In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected at the top but insulated at its base-terminals specifically by a spark-gap; of an electric circuit connected to the antenna-terminals and forming with the antenna-loop a closed circuit; a secondary closed circuit including transmitting apparatus and operatively associated with the first closed circuit; receiving means operatively associated with the first closed circuit; and means for cutting out the receiving means when the transmitting apparatus is in use.

13. In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected atthe top but insulated at its base-terminals; of an electrical circuit connected to the antenna base-terminals and forming with the antenna-loop a closed circuit approximately equivalent in length to a half-wave length or a multiple thereof; a secondary closed circuit operatively associated with said first closed circuit; a receiving device operatively associated with said second closed circuit; means for making the first closed circuit most strongly responsive to the transmitted waves; and means for adjusting the period of the second closed circuit.

14. In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected at the top but insulated at its base-terminals; of an electric circuit connected to the antenna base-terminals and forming with the antenna-loop a closed electrical circuit; an adjustable inductance in one branch of said closed circuit; and a receiving device operatively associated with the branch of said closed circuit which contains said inductance.

15. In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected at the top but insulated at its base-terminals specifically by a spark-gap; of a circuit connected to the antenna base-terminals and forming with the antenna loop a closed electrical circuit; a transmitting apparatus and an adjustable inductance therefor, operatively associated with one branch of said closed circuit; a receiving apparatus and an adjustable inductance operatively associated with the other branch of said closed circuit; and means for cutting out the receiving apparatus when the transmitting apparatus is in use; both said inductances cooperating independently of the operation of the transmitting apparatus when the receiving apparatus is inuse.

16. In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected at the top but insulated at its base-terminals; of a circuit connected to the antenna base-terminals and forming with the antenna-loop a closed electrical circuit; adjustable inductance in said closed circuit; a receiving apparatus operatively associated with said closed circuit; and a circuit other than said closed circuit, which includes an indicating means for the receiver.

17 In an electrical-wave system of communicating intelligence, the combination with an antenna-loop connected at the top but insulated at its base-terminals; of a circuit connected to the antenna base-terminals and forming with the antenna-loop a closed electrical circuit; adjustable inductance in said closed circuit; a secondary closed circuit, and receiving means connected therein; and a third circuit which includes the receiving means and indicating means therefor.

In testimony whereof I have hereunto afiixed my signature, this 23d day of January, 1903, in the presence of two witnesses.

LEE DE FOREST.

Witnesses:

M. W. NOLAN, H. L. REYNOLDS. 

